Already did, and will post here any response I get from OPPO. Fortunately, the output of the above procedure works consistently on the BDP-105. I now have a dozen albums (as single-file dff files and cue files) on a drive and the OPPO reads them fine. Going from ISO to diff+cue takes less than a minute, so I can't complain. Tomorrow I will post some before (problematic)/after (glorious) cue files you all can use as templates.
Two new issues were discovered. First, if your audio file name in the cue file has strange characters (e.g., accented letters), the BDP-105 will not be able to find the audio file in the directory. It is as if its file system or the cue parser (but not both) strips the accents, so there is no longer a match and you get the "cannot find associated file" message.
The second issue really has me puzzled. You might have noticed that 7-zip can open some SACD-R ISO files, whereas others it cannot. I never thought much of this, because the BDP-105 (prior to the latest firmware) would play disks burned form both types of ISOs just fine. However, now that the new BDP-105 firmware prevents it from reading either type of disk, we have to generate the audio file w cue. Well, it seems that SACD_extract only works with the latter type of ISO files. When I process a SACD-R ISO that 7-zip can also peek into, I get a dff file and cue file that the OPPO can recognizes just fine, except I get very loud digital white noise. This is a SACD_extract issue, not a BDP-105 cue issue, but in case anyone has come across this before: what is the difference between a SACD-R ISO that 7-zip can open, and one that 7-zip cannot? It made no difference to the BDP-105 (old firmware), but it sure makes a difference to SACD_extract.